1. Field of the Invention
The present invention is directed to an arrangement for coupling and decoupling a drive mechanism from an adjustable patient positioning plate, of the type used in a medical diagnostic or treatment system.
2. Description of the Prior Art
Patient positioning tables are employed in medical systems in order to position examination subjects, particularly patients, for specific medical examinations and/or treatments. An exact adjustment and positioning of the positioning plate of such a patient positioning table must be assured in radiological examinations, particularly computed tomography examinations, magnetic resonance examinations as well as radiation treatment, but also for other treatments, whereby a subject must be positioned exactly, particularly reproducibly, with resect to a treatment instrument or device. For adjustment of the positioning plate, it is known to provide a drive that has a toothed belt guided on wheels at which engages the positioning plate for adjustment. A drive motor is connected to at least one of these wheels via a controllable coupling means. In the coupled state, it is cosequently possible to adjust the positioning plate via the drive at least along its longitudinal axis. A precise positioning of the patient for the diagnostic or therapy system is consequently possible. In addition, it makes the work of the medical personnel easier since no exertion is required. In order to make it possible to quickly adjust the positioning plate given a power outage or for medical treatment of the patient, the drive can be decoupled from the wheel, so that the positioning plate is adjustable at least along its longitudinal axis. This is then particularly advantageous when the patient is introduced into a tube or a tunnel for the treatment, as is required for computed tomography or magnetic resonance examinations. When the patient is to be examined or treated further, e.g. after the medical treatment, then the patient must be positioned with the positioning plate optimally exactly at the original examination treatment location. The use of encoders and reference switches at the drive in connection with the drive means and/or the positioning plate is known.
The adjustment of the positioning plate into the examination position ensues on the basis of the signals of the encoders via the drive motor and is controlled by software.
German OS 3126 643 discloses a radiation diagnosis device having a means for adjusting a positioning device for an examination subject using a stepping motor in conjunction with a spindle.
An object of the present invention is to implement a coupling arrangement of the type initially described wherein the positioning plate can be decoupled from the drive arrangement in a simple fashion, and wherein a precise re-coupling to the drive arrangement as well as an exact re-positioning of the positioning plate are possible after decoupling and adjusting the positioning plate.
The above object is achieved in accordance with the principles of the present invention in a patient positioning apparatus having a motorized drive and an adjustable positioning plate, and a coupling arrangement directly connected between said drive and said positionable plate which is selectively operable to couple said drive to said plate, allowing adjustment of the plate along its longitudinal axis by the drive, and to decouple the drive from the plate, thereby allowing manual adjustment of the positioning plate. Coupling and decoupling takes place by making and breaking a coupling retention. The retention can be produced magnetically or mechanically.
An advantage of the invention is that the positioning plate is adjustable at least in the direction of its longitudinal axis via the drive arrangement as well as by hand. Using a coupling arrangement to cancel a retention connection between the drive arrangement and the positioning plate, the positioning plate is adjustable at least along its longitudinal axis via the drive arrangement given a retention connection, and by hand given a canceled retention connection. The coupling arrangement inventively acts directly between the drive arrangement and the positioning plate, so that slackness or imprecision do not arise, as are caused in convention devices by the elasticity of the toothed belt or due to the graduation of the encoder.
It is advantageous to implement the coupling arrangement as a magnetic arrangement, particularly having at least one permanent magnet. Such permanent magnets are inexpensive, in that they do not require energy in order to produce or cancel the magnetic fields.
The coupling arrangement can have at least one magnetic plate and a permanent magnet, with the plate and the permanent magnet being rotatable relative to one another around an axis, the rotation ensuing via a lever. Coupling is thereby achieved in a simple fashion between the plate and the permanent magnet, and thus between the positioning plate and the drive arrangement in a simple and precise way.
As an alternative to magnetic coupling, a mechanical coupling with limited linkage play can also be used.
It is particularly advantageous, when the drive arrangement has a drive mechanism that engages and rotates a threaded spindle for longitudinal displacement of the positioning plate. The spindle is in communication with the positioning plate via a spindle nut and the coupling arrangement. A very precise positioning of the positioning plate is possible via the spindle in conjunction with the spindle nut.
In a first version of an exemplary embodiment of the invention, a carrier engages the spindle nut, and extends at least approximately vertically to the longitudinal axis of the spindle, and has at least one area with magnetic material. At least one magnetic element allocated to the area is arranged at the positioning plate, the magnetic element being in communication with a lever, with which it can swivel around the swivel axis, and the magnetic connection can be neutralized by swiveling the lever. According to an alternative version of the invention, at least one carrier extends from the spindle nut at least approximately vertically to the longitudinal axis of the spindle for at least one magnetic element, and at the positioning plate, at least one magnetic area allocated to the magnetic element is provided. The magnetic area is in communication with a lever, with which it can be swivelled around the swivel axis, and the magnetic connection can be canceled by swivelling the lever. Thus, a precise coupling and decoupling between the drive arrangement and the positioning plate is assured in a simple fashion.
In order to assure symmetrical forces and consequently to avoid a tilting of the positioning plate, the spindle and the spindle nut, it is advantageous when the coupling arrangement has two sub-arrangements on both sides of the center axis of the positioning plate that are linked to one another via the lever.
To compensate tolerances, it is advantageous when the magnetic devices, or the magnetic areas, are seated so as to be adjustable in a direction along the swivel axis.